Update Image.cs

Before reading stream for header , position should be changed to 0 if the passed stream were read before

Former-commit-id: 39b39e2f2ff275215cccf4d55ed65652abf62109
Former-commit-id: 7ef123922caef2f00577b2262313e9f2d6228fff
Former-commit-id: 98be9a262b460d79f04206b53c8ed83f307b3948

src/ImageProcessorCore/Image.cs

@@ -246,7 +246,8 @@ namespace ImageProcessorCore
                 if (maxHeaderSize > 0)
                 {
                     byte[] header = new byte[maxHeaderSize];
-
+                    
+                    stream.Position = 0;
                     stream.Read(header, 0, maxHeaderSize);
                     stream.Position = 0;